Banking on BARC
Thanks in part to the work of weed ecologist John Teasdale, the USDA Agricultural Research Service's oldest experiment station is doing some of the agency's most forward-looking work.

By Laura Sayre
July 15, 2005

Certified organic
at ARS

Beltsville researchers have been doing research related to organic farming systems for more than ten years. But how has National Organic Program implementation in 2002 affected the research context? How much certified organic research is going forward at BARC, and at ARS generally?

Carolee Bull, a research plant pathologist based at an ARS station in Salinas, California, has been cooperating with Mike Jawson, ARS National Program Leader for Integrated Farming Systems, and others to find answers to those questions. Bull reports that there is now a total of about 70 certified organic acres at ARS research stations in Iowa, Maryland, California, Florida, Texas, Georgia, and Minnesota. An unknown additional amount of land is probably readily certifiable.

A key stop on Teasdale's BARC field tour is a 22-acre field that recently became the center's first certified organic research acreage. This spring, Teasdale and his colleagues established their first experimental plots on the site, a study of weed tolerance by organic soybeans with different growth habits.

A total of six cultivars, some of them developed here at BARC by geneticist Tom Devine, are being evaluated in paired plots: a tall soybean vs. a standard-height soybean; an early developing soybean vs. a standard developer; and a large leaf vs. a normal-sized leaf. All plots are receiving identical cultivation treatments between the rows, but the in-row area—where weeds are most difficult to manage—is being subjected to three different treatments: all weeds are removed; crop plants removed; and additional weed seeds added.

Although the facility in Salinas is so far the only ARS station with a dedicated organic specialist position—research horticulturalist Eric Brennan—Teasdale notes that his lab and others began collaborating with local certified organic farmers as early as 1999. That strategy continues: Teasdale's lab is currently participating in an organic high-tunnel tomato production evaluation, funded in part by SARE and replicated at five organic farms across the state of Maryland.

Bull, who in 2002 conducted a survey of ARS scientists to determine levels of interest and activity in organic, found that 81 scientists system-wide were "conducting research in explicitly organic systems" and another 107 were interested in organic systems. In January 2005, the agency convened a meeting in Austin, Texas, to begin formulating an ARS organic research agenda—a step that Bull thinks should give a needed administrative imprimatur to organic research efforts.

In time, Bull says, "we could be the premier organic research institution that is federally funded. As long as the scientists on the ground communicate with one another, we could make quantum advances in organic theory as well as in production practices. We should be able to ask the big questions."

Brennan, who also has a total of 22 acres either certified organic or in transition, agrees there's a lot of interest in organic agriculture among agency scientists and administrators and that the Austin meeting "was an important first step." A major challenge to establishing more certified organic research acreage, he feels, is that particularly for horticultural crops, "organic management is more intensive, and so organic research is more expensive."

Because organic management requires different tools and skills, it will take time for researchers and technicians—just as it takes time for farmers—to make the transition. --LS

























"I think for minimum-till organic systems to work, a rotation out of annual crops and perhaps even a tillage rotation will be important to lower seed banks and clean up perennial weeds."




























































"We've gotten to the point where we can say, yes, we can provide on-farm nutrient sources, but from the standpoint of keeping the N on the farm—that's still a big challenge."

Most of one wall of John Teasdale's office at the Beltsville Agricultural Research Center is occupied by a large-scale color satellite image of the surrounding area. On it, you can see how the fields, barns and greenhouses of the USDA Agricultural Research Service's flagship experiment station are ringed and threaded by the housing developments, shopping malls and thruways of greater Washington, D.C.

Teasdale's been here long enough—26 years—to have witnessed a good deal of that suburban encroachment. Today, when he walks out the front door of the building that is home to the Sustainable Agricultural Systems Lab, which he heads, and looks south, he can see the nearest IKEA rising above the trees. Although the research station still commands more than 7,000 acres, and lies adjacent to another 20,000 acres of undeveloped federal property, the pulse of the Beltway is omnipresent.

But Teasdale can also testify to other changes over the last quarter century, changes less glaring and more broadly beneficial. While his own interests moved toward sustainable agriculture early on, in more recent years he's seen a dramatic increase in research related to making agriculture more profitable for farmers and less damaging for the environment.

"In the 1950s and '60s, ARS did mostly breeding work," Teasdale explains. "Now the seed industry has taken over most of that. I was hired to do tests of chemical weed control products. Then the molecular biology kick arrived and lots of people left the field and went into the lab. I was pretty much left alone out here." But he's emphatically not alone any more, as a tour of the BARC research fields makes clear.

Branching out

Originally from Minnesota, Teasdale received his Ph.D. in agronomy from the University of Wisconsin in 1978 and was hired by the USDA straight out of graduate school. "Most of my first six or seven years were spent working with herbicides," he recalls, taking chemicals developed for corn and soybeans and testing their applicability for various horticultural crops.

"Especially for the smaller crops, the liability is high and the acreage is low, so there's not much incentive for the companies to invest there," he explains. Teasdale showed, for instance, that when cantaloupes were grown on plastic mulch, atrazine could be used between the rows without causing damage to the crop.

By the mid 1980s, however, Teasdale decided it was time to stretch his wings. Herbicide companies, he realized, had little incentive to pursue labeling even if application data were available. "Only two things I worked on ever got a label," he says wryly. He also decided that as a federal employee, he had a responsibility to pursue research of the broadest possible long-term benefit—"research that wasn't being done elsewhere."

Teasdale began by observing that the most effective weed management strategies involved a combination of chemical and cultural controls, including planting methods, cultivation tools and—crucially—cover crops. For Teasdale, developing horticultural applications for agronomic chemicals demanded an integrated approach. As he puts it, "You thought a lot about how the cultural control was affecting the crop, how the herbicide affected the cultural control. . . and how to use factors like row spacing and crop density to speed up the competitiveness of the crop."

Working on cover crops, in particular, drew Teasdale toward studying the rest of the agroecological system, in all its beguiling complexity. "Because cover crops have so many impacts on cropping systems, from soil moisture levels to soil temperature levels to nutrient movement, one's research inevitably starts to branch in to all those different areas," he observes. "And I think we've barely scratched the surface when it comes to understanding all those factors."

Interdisciplinary, systems-oriented research

Teasdale's impulse toward multidisciplinary investigation was facilitated by a reorganization of BARC's human resources in the late 1990s. Formerly, the researchers were sectioned off by discipline: weed scientists, soil scientists, vegetable crop specialists, agronomists, and so on. In 2000, researchers from all these fields and more were regrouped into the Sustainable Agricultural Systems Lab, which today consists of about 45 scientists and technicians.

But the scientists were moving toward a systems-oriented approach well before that. In 1993, Teasdale and his colleagues set up the Sustainable Agriculture Demonstration Project, a long-term study focusing on reduced tillage. Because of the site's topography—a two to 15 percent slope, running in both directions across the field—the researchers sought to prioritize soil conservation as well as crop yields and net returns in their experimental design. They settled on four different management systems, all applied to a two-year rotation of corn/winter wheat/soybean:

  1. a conventional no-till system with standard herbicide and fertilizer inputs;
  2. a crown vetch "living mulch" system developed by Nathan Hartwig, a professor of weed science at Penn State University, also with standard herbicide and fertilizer inputs;
  3. a modified conventional system, in which cover crops were substituted for some of the herbicide and fertilizer inputs (hairy vetch before corn and wheat before soybeans);
  4. an organic, reduced tillage system, with crimson clover and cow manure substituted for fertilizer inputs and cultivation for herbicide inputs.

The SADP is now being brought to a close, Teasdale explains, "because the general outcome was clear." Although the crown vetch system performed well in years with adequate rainfall, it did poorly compared to the conventional no-till in dry years. The cover crop and organic/manure systems did the best job of returning nutrients and organic matter to the soil, but the organic system suffered from heavy weed pressure. This led to lower average yields for the organic system, although reduced inputs resulted in only slightly lower net returns—even without the inclusion of an organic premium. (Detailed results from the SADP can be found in the American Journal of Alternative Agriculture 15,2: 79-87 [2000].)

Interestingly, Teasdale notes, a post-experiment uniformity study (conventional no-till corn grown across all plots) is showing that "the two treatments that did the worst in themselves"—the crown vetch and organic treatments—"are giving the best effects now." In other words, they did the most to build and improve the soil, resulting in healthier crops and better long-term yields. "What that says is that the organic system would have done well if we could have controlled the weeds."

Other long-term organic vs. conventional systems trials, including The Rodale Institute's Farming Systems Trial and the Integrated Cropping Systems Trial at the University of Wisconsin, have used a similar grain crop-based organic system with similar results, Teasdale points out. "We had too many weeds because we tried to just take a conventional agronomic rotation" and make it organic. "We needed a more diverse rotation with a hay crop. Otherwise, the weeds will just kept getting worse."

Lessons from the SADP have been folded into BARC's other long-term trial, known as the Farming Systems Project. The FSP was also initiated in 1993, but unlike the SADP it began with a three-year uniformity study in which no-till conventional corn was grown across the entire site and data were collected on growth rates, yields, and soil variables. Experimental plots for the FSP itself were then laid out to maximize homogeneity across plots.

Today the FSP consists of five cropping regimens, two conventional and three organic:

  1. a conventional, standard tillage three-year corn-soybean-wheat rotation;
  2. a conventional, no-till three-year corn-soybean-wheat rotation;
  3. an organic two-year corn-soybean rotation;
  4. an organic three-year corn-soybean-wheat rotation;
  5. an organic four-year corn-soybean-wheat-red clover/orchard grass hay rotation.

Each system was tested from all possible starting points within the rotation sequence. All of the systems included cover crops—rye before soybeans and hairy vetch or crimson clover (or hay, in the third organic system) before corn. The organic systems used both standard tillage and reduced tillage, depending on the year, with cover crops mowed or rolled prior to no-till planting.

Given the results of the SADP, Teasdale has been especially interested in the ability of the different organic rotations in the FSP to manage weeds. What they've found, he explains, is a "lower seed bank and better weed control of the most troublesome weeds in our organic plots in the longer, more diverse rotations." (A full analysis can be found in Agronomy Journal 96: 1429-35 [2004]). The four-year organic rotation beginning with hay did the best job of keeping weed seed bank levels low.

"I think for minimum-till organic systems to work, a rotation out of annual crops and perhaps even a tillage rotation will be important to lower seed banks and clean up perennial weeds," Teasdale concludes.

The many uses of cover crops

Long-term, multidisciplinary field experiments like the SADP and the FSP require the collaboration of many scientists. Soil scientist Michel Cavigelli, agronomist Mark Davis, research chemist Jeff Buyer and microbiologist Patricia Millner are just a few of Teasdale's colleagues who have worked on these studies. One of the strengths of BARC and the Sustainable Ag Systems Lab (SASL) is that they allow and encourage that kind of interdisciplinary interaction.

Another of Teasdale's colleagues is Aref Abdul-Baki, a plant physiologist who has done extensive work on warm-season cover crops such as sunn hemp, and who has sought to develop cover-crop-based alternatives to methyl bromide for large-scale vegetable growers in Florida. (Vegetable producers use the soon-to-be banned chemical as a soil fumigant to eliminate potentially crop-damaging nematodes.) Together, Teasdale and Abdul-Baki have studied the allelopathic effects of cover crops like hairy vetch, demonstrating, for instance, that the most powerful weed suppression appears to result from a synergy between the phytotoxins released by the cover crop residue and its action as a physical barrier.

In the field we run into entomologist Don Weber, who came to BARC four years ago and is currently studying the effects of cover crop mulches on Colorado potato beetles. "When I started looking at cover crops and mulches in the 1980s, that was an effect I noticed right away," comments Teasdale, referring to reduced CPB damage on mulched potatoes. "I mentioned it to the entomologists, but nobody was interested. Now at last we have people like Don, who are interested."

In some parts of the field the difference was dramatically visible: unmulched plants skeletonized by the fat orange instars; a few rows away, mulched plants almost untouched. "There are at least four different things that could be going on," Weber explains enthusiastically. The mulch could be changing the microclimate, for instance by lowering soil temperatures; it could be altering the biochemistry of the potato foliage; it could be directly impacting the potato beetle in some way; or it could be affecting the pest's natural enemies. "There's a carabid beetle that's a specialist predator on the CPB," Weber adds, brushing aside some cover crop residue and pointing out a small, blue-black beetle.

Elsewhere on the farm, Teasdale tells us, Weber's trialing potatoes with a variety of different cover crops, including crimson clover, hairy vetch, and rye, and is also experimenting with different ways of handling the transition from cover crop to crop. "Since potatoes go in so early, you don't get much biomass from the cover crop if you kill it at the time of planting," Teasdale points out. "Maybe we can develop a system in which you plant into the standing cover crop and then mow when the potatoes start to emerge."

In the 1990s, an SASL study of tomatoes grown on hairy vetch mulches found that the mulched plants senesced significantly later in the season than unmulched plants. Subsequent experiments have sought to clarify the underlying mechanism at work. A key question is how the vetch residue, which is almost completely decomposed by mid-season, promotes crop plant health at the end of the season. This year, the researchers are comparing tomato plots mulched with vetch tops only, vetch roots only, rye tops, rye roots, black plastic, white plastic, or not mulched at all.

"We think the effect has to do with more than just the N levels supplied by the vetch," Teasdale comments. "Dr. Autar Mattoo, a molecular biologist in our lab, has shown that the cover crop mulch influences the expression of many important genes in the tomato plant."

Cover crops and N utilization

A final, fundamental role for cover crops, of course, is to supply fertility for crops. While it's well established that cover crops can supply all the nitrogen needed by a cropping system, much remains to be learned about how best to manage that supply.

"That's really what I see as one of the big challenges of sustainable agriculture," says Teasdale. "We've gotten to the point where we can say, yes, we can provide on-farm nutrient sources, which means they're more sustainable in terms of the environmental costs of being produced elsewhere and transported to the farm, but from the standpoint of keeping the N on the farm—that's still a big challenge."

Because nitrogen supplied by cover crops and composts needs to mineralize in order to become available to crops, calculating and timing its availability is trickier than with synthetic N sources. No crop is 100 percent efficient at utilizing available N, moreover—"corn is only 50 percent efficient at using available N, and tomatoes are more like 20-30 percent," Teasdale notes—so you have to use too much in order to have enough. The key is to capture the excess before it can leach out of the system and become a pollutant.

"Say you have 150 pounds of N in a hairy vetch cover crop, the amount of N that gets taken up by the crop is quite small. A number of different people have shown that experimentally—a substantial part is lost to leaching and to the atmosphere. With manure and compost, it's the same situation. It's a big challenge to understand the mineralization process, because it's microbially driven."

One solution, Teasdale continues, is to revise the definition of optimum crop production, since the yield-response-to-N curve is not linear—there's a diminishing return as you add more nitrogen to the system. "People are thinking now that if you drop back a bit, you would only slightly lower yields but put significantly less surplus N into the environment."

Another is "to use cover crop mixtures where the combination of C and N is better balanced, [so] the N becomes temporarily sequestered," an effect that's fairly well established scientifically, Teasdale says. The optimum carbon-to-nitrogen ratio seems to be between 20:1 and 30:1, he adds.

Of course, a lot of farmers do use a rye-vetch mixture as cover crop, which is a good way to achieve that C:N balance. Like other researchers working on organic cropping systems, however, Teasdale is keenly interested in the prospect of organic no-till, and "for organic no-till, the mixture is harder to manage," for various reasons. "You may get more biomass for weed suppression [with a mixture], but all that additional residue can interfere with planting operations." If the planting row falls right on the top of a rye row, moreover, the rye root mass can inhibit germination.

"But none of those problems are insoluble," he emphasizes. "They just require more work." Fortunately, BARC has a dedicated team tackling them from a broad range of disciplinary perspectives.

Laura Sayre is senior writer for